1 . —I wonder__________ Mary has kept her figure after all these years.
—By working out every day.

A．Where

B．how

C．why

2 . _____ was known to all , William had broken his promise ______ he would give us a rise.

A．As; which

B．As; that

C．It; that

3 . The man didn’t know ______ the thief broke into the house and stole all his valuable things.

A．it was when that

B．when it was that

C．that it was when

4 . The number of_____ in our class ____ fifty.

A．student; is

B．the student; are

C．the students; is

5 . —English has a large vocabulary, hasn't it?
—Yes. _____ more words and expressions and you will find it easier to read and communicate。

A．Know

B．Knowing

C．To know